1. Field of the Invention
The present invention relates to a method for handoff of a portable terminal between heterogeneous wireless networks, and more particularly, to a method for handoff of a portable terminal between heterogeneous networks for rapidly performing vertical handoff of the portable terminal between the heterogeneous networks of which service areas are overlapped.
2. Description of the Related Art
A next-generation network is expected to be evolved to a type in which various Internet protocol-based wireless networks have overlapped service areas. That is, an environment is created in which the service areas of the wireless networks having different characteristics, which interwork with each other are hierarchically overlapped. The heterogeneous wireless network environments have different wireless characteristics and the service areas of the wireless networks that interwork with each other are hierarchically overlapped, such that various vertical handoff methods are proposed in order to flexibly access an optimal network that is selected depending on the position of a service user, a radio wave environment, a service characteristic, and a user preference, etc.
Among various vertical handoff methods, a method of determining handoff on the basis of positional information of the portable terminal determines the handoff by considering only the positional information of the portable terminal in the environment in which the heterogeneous networks are overlapped. Since the handoff is performed without considering a confusion rate or data traffic of each of the overlapped network, network resources cannot be efficiently utilized. Further, even though a predetermined network can be selected by considering a user's desired service quality and a network service charge in the environment in which the heterogeneous networks are overlapped, a cost saving effect which can be achieved by user selection, etc. cannot be achieved by considering only a strength value of a received signal.
Meanwhile, in a method of determining the handoff by considering information on a movement velocity of the terminal, since a one-time reference velocity threshold value is used, the handoff is determined depending on the movement velocity when the velocity of the terminal is temporarily decreased, for example, when the terminal stops a traffic signal lamp. Therefore, there is a high possibility that a ping-pong effect will occur in the handoff using the reference velocity threshold value.
As such, since the known vertical handoff methods should make many assumptions or reconfigure the current network environment, an additional development cost is generated. Further, the terminal should have various network interfaces in order to support the heterogeneous network handoff. Accordingly, since the terminal should perform an operation for collecting network information corresponding to all network interfaces, power consumption increases.